Abstract: Systems for treating water, e.g., mobile deionization systems, are disclosed. The system includes a system inlet connectable to a source of water to be treated; a water distribution manifold connected to the system inlet and including a plurality of valves structured and arranged to provide a configurable flow path along the water distribution manifold; a plurality of water treatment vessels each having an inlet and an outlet connected to the water distribution manifold; and a system outlet connected to the outlet of a last of the plurality of water treatment vessels. The plurality of valves are selectively operable to provide for sections of the water distribution manifold to switch between flowing water into one or more of the plurality of water treatment vessels or receiving water from the one or more of the plurality of water treatment vessels. Methods of treating water using the systems are also disclosed.